1. Field of the Invention
The present invention relates to a diamond film formation method and a film formation jig thereof, and more particularly, it relates to a film formation technique for forming a diamond film on an interior surface of a metal material comprising a hollow body and a recess.
2. Description of the Related Art
Diamond has a bandgap of about 5.5 eV at room temperature, and has good semiconducting properties and optical properties in addition to mechanical, chemical and thermal properties, and attention is therefore focused on diamond as a semiconductor material.
As techniques using diamond as a semiconductor material, for example, cold cathode discharge devices have been disclosed (refer to JP-A 2002-298777 (KOKAI) and JP-A 2003-132850 (KOKAI)). In these techniques, diamond with high secondary electron emission efficiency and high resistance to sputtering can be used to provide cold cathode discharge devices with high luminous efficiency and longer lives. These cold cathode discharge devices have simple structures without heating filaments, are easily reduced in size, can be used at a low temperature and have comparatively long lives, such that they are widely used for illumination, backlights of liquid crystal devices, etc.
Furthermore, in order to improve the efficiency in secondary electron emission from the surface of diamond, there has been disclosed an electrode made of a metal material in which a diamond layer is formed on a cup-shaped or tubular interior surface (e.g., refer to U.S. Pat. No. 5,880,559).
However, when a diamond film is to be formed on the interior surface of the cup-shaped or tubular metal material, a thick film of diamond tends to be formed in an outer peripheral portion of the metal material if the CVD method is used, and it has thus been difficult to form a diamond film on the interior surface of the cup-shaped or tubular metal material.
As described above, it is desirable that, as a cold cathode used in the cold cathode discharge device, a diamond film be formed on the interior surface of the cup-shaped or tubular metal material to improve the efficiency in the secondary electron emission from the surface of diamond, but it has been difficult in principle to form a diamond film only on the interior surface by the CVD method. Therefore, it has been desired to develop a film formation method which makes it possible to efficiently form a film of diamond on the interior surface of the cup-shaped or tubular metal material.